Integrated circuits may be formed on a semiconductor substrate such as a silicon wafer or other semiconducting material. In general, layers of various materials which are either semiconducting, conducting or insulating are used to form the integrated circuits. By way of example, the various materials are doped, ion implanted, deposited, etched, grown, etc. using various processes. A continuing goal in semiconductor processing is to continue to reduce the size of individual electronic components thereby enabling smaller and denser integrated circuitry.
One technique for patterning and processing semiconductor substrates is photolithography. Such includes deposition of a patternable masking material commonly known as photoresist. These materials can be processed to modify their solubility in certain solvents, and are thereby readily usable to form patterns on a substrate. For example, portions of a photoresist layer can be exposed to actinic energy through openings in a radiation-patterning tool, such as a mask or reticle, to change the solvent solubility of the exposed regions versus the unexposed regions compared to the solubility in the as-deposited state. Thereafter, the exposed or unexposed regions can be removed, depending on the type of photoresist processing, thereby leaving a masking pattern of the remaining photoresist on the substrate. Areas of the underlying substrate next to the masked portions can be processed, for example by etching or ion implanting, to effect the desired processing of the substrate adjacent the masking material. In certain instances, multiple different layers of photoresist and/or a combination of photoresists with non-radiation sensitive masking materials are used.
The continual reduction in feature sizes places ever greater demands on the techniques used to form the features. For example, photolithography is commonly used to form patterned features, such as conductive lines and contact openings. A concept commonly referred to as “pitch” can be used to describe the sizes of the features in conjunction with spaces immediately adjacent thereto. Pitch may be defined as the distance between an identical point in two neighboring features of a repeating pattern in a straight line cross section, thereby including the maximum width of the feature and the space to the next immediately adjacent feature. Due to factors such as optics and light or radiation wave length, photolithography techniques tend to have a minimum pitch below which a particular photolithographic technique cannot reliably form features. Processing techniques to overcome these limitations include pitch multiplication and multiple patterning of the same layer, or of different layers, of photoresist.